The present invention relates to a monitoring system for regulating a pressurized pipeline wherein a pilot valve senses departures of the pipeline pressure from a normal range and responds by closing a shut-off valve in the pipeline and wherein the pilot valve subsequently resets itself automatically when the pipeline pressure returns to normal.
By way of specific example, such a monitoring system may be used to open and close a shut-off valve in a high pressure natural gas distribution line in response to changes in demand downstream from the shut-off valve. The shut-off valve is spring biased to close and has a control cylinder into which pressurized control fluid may be introduced to open the shut-off valve. Pilot means senses changes in the pipeline pressure downstream from the shut-off valve and vents the control cylinder of the shut-off valve to close the shut-off valve when the pipeline pressure rises to a predetermined magnitude and subsequently admits control fluid to the control cylinder of the shut-off valve to open the shut-off valve when the pipeline pressure drops below the predetermined magnitude.
During the daytime, when the demand for natural gas is low, the pressure downstream from the shut-off valve stays high enough to keep the shut-off valve closed. As evening approaches, the demand for natural gas increases with subsequent decay of the pipeline pressure and the pilot means responds by opening the shut-off valve. Later the demand for natural gas decreases with consequent increase in the pipeline pressure to cause the shut-off valve to be again closed.
Such a regulating monitoring system is to be distinguished from a safety monitoring system wherein a monitor pilot cooperates with an actuator pilot to close a shut-off valve in a pipeline in an emergency, for example, when a dangerously high pressure surge occurs in the pipeline or when rupture of the pipeline downstream from the shut-off valve causes the pipeline pressure to drop. After the cause of such an emergency is corrected, the actuator pilot of the control system must be reset by hand to restore the pipeline to service. Thus, the safety monitoring system forces responsible personnel to take note of an emergency. It is apparent that automatic resetting of the actuator pilot would defeat the purpose of a safety monitoring system.